The primary research aim of this study is to relate the relatively new areas of cytogenetics and human behavior genetics to problems in normal human development and psychopathology. We are investigating the nature of the relationship which might exist between sex chromosome aneuploidies in males (XXY, XYY) and subsequent personality development. Male infants with sex chromosome abnormalities are being ascertained through a chromosomal survey of consecutive newborn males. This allows for a second research aim of establishing the prevalence of chromosomal abnormalities in the newborn population. The aneuploid and control males are being followed in a long-term developmental study in order to determine the behavioral consequences related to sex-chromosome aneuploid states.